Methods and apparatuses for electrophotographic printing are known. Electrophotographic printing generally includes imparting an image on a final receptor by forming a latent image on selectively charged areas of a photoconducter such as a charged drum, depositing a charged toner onto the charged areas of the photoconductor to thereby develop an image on the photoconductor, and transferring the developed toner from the charged drum under heat and/or pressure onto the final receptor. An optional transfer member can be located between the photoconductor and the final receptor. Examples of electrophotographic apparatuses and methods are disclosed in U.S. Pat. Nos. 5,276,492; 5,380,611; and 5,410,392. The '492 and '392 patents both disclose that a preferred toner is a liquid toner comprising carrier liquid and pigmented polymeric toner particles which are essentially non-soluble in the carrier liquid at room temperature, and which solvate in the carrier liquid at elevated temperatures. Examples of such liquid toners are disclosed in U.S. Pat. No. 4,794,651. The '492 patent and the '392 patent both disclose that the toner image can be transferred to a receiving substrate such as paper ('492 patent: column 7, lines 19-20; '392 patent: column 4, lines 57-58). While having their own utility, paper substrates are not desired for all applications and uses. The '611 patent discloses that the toner image can be transferred to a receiving substrate such as a transparency, without disclosing any particular composition of a transparency (column 4, lines 17).
It is also known that certain polymeric and ionomeric compositions are suitable for use with some printing methods and apparatuses. For example, flexographic printing on films made from SURLYN brand ionomeric resin, available from E. I. du Pont de Nemours & Company, Wilmington, Del. has been suggested. See Brooks & Pirog, Processing of Surlyn.RTM. Ionomer Resins by Blown and Cast Film Processes, p. 18, Du Pont Company, Plastics Department, Polyolefins Division, Technical Services Laboratory. U.S. Pat. No. 5,196,246 discloses a wall decorating system that, in one embodiment, includes a SURLYN blend film that can be printed by etching, embossing, flexographic printing, silk screening, or gravure processes (column 14, lines 16-19).
Conventional printing processes include flexographic, gravure, and screen printing. These processes require a long time to make printing patterns, such as printing plates or gravure cylinders. Furthermore, the printing equipment needed for such processes is rather expensive. Such printing processes are not practical for short run print-on-demand type printing.
Polycarbonate films are well known for their high impact resistance, good thermal moldability, and excellent lens-like clarity. Many types of products in the electronics, appliance, and automotive industries such as cellular phones, air conditioners, and automotive dial displays, etc. therefore use polycarbonate sheets as a graphic overlayer.
However, these polycarbonate graphic overlays are traditionally prepared with solvent based screen printing processes. These processes not only require a long time to make artwork and to prepare printing screens, but they are also less environmentally friendly. These products are not practical for short run print-on-demand type printing. Recently developed Indigo and Xeikon print processes, however, yield high quality images and are suitable for short run print on demand printing processes.
The commercially available durable product for electrophotographic digital imaging comprises an imageable modified PET, which is then modified by the application of a polycarbonate layer. In other words, a layer of polycarbonate previously could not be directly imaged with such methods. Instead a layer of modified PET was imaged and subsequently covered with a layer of polycarbonate. The polycarbonate (PC) was attached to the imaged PET with a layer of pressure sensitive adhesive. However, according to the present invention, a novel PC imaging medium has been provided which can be imaged directly using electrophotographic printing technology. The novel imaging medium of the invention not only requires fewer steps than the known product but also uses less raw material.
Short run, print-on-demand type printing is becoming increasingly popular. Printers capable of providing such short run print on demand printing include those developed by Indigo Ltd. and those developed by Xeikon N.V. The Indigo printers can employ electrophotographic liquid toner whereas the Xeikon printers employ dry toner.
Commercially available polycarbonate films which are untreated cannot be printed with an Indigo printer. A special solvent based polyamide coating (such as that available from Indigo Ltd. under the name Topaz) is usually required in order to yield acceptable printing with the Indigo printer. However, the image printed over such a coating typically exhibits poor Taber abrasion resistance (i.e., below 6).
Commercially available polycarbonate films can be readily printed with a Xeikon printer. However, the resultant images demonstrate inadequate Taber abrasion resistance (i.e., below 6).